Making Characters, All the Way Up
One of the things I did at Wizards back in the day was create and then maintain what we called the "Pre-Fab Four:" Mialee the wizard, Jozan the cleric, Tordek the fighter, and Lidda the rogue. Each one lived in its own Excel spreadsheet, with one tab for each level. Whenever we needed a party for a playtest (or just for benchmarking), we'd print out the relevant level. It wasn't the prettiest character sheet, and it wasn't the smartest spreadsheet (though it did do basic calculations for you). It worked, though—we used the Pre-Fab Four year after year.
For 3.0 we actually had all of the "iconics"—Krusk, Vadania, etc.—statted up 1-20. I did first drafts on about half of those and second drafts on nearly of all 'em. Whew!
And along the way we killed a lot of trees. The spreadsheets had a bug we never could squash where the "Number of Copies" field always had an arbitrarily large number…19,000 or so. You had to remember to fix that each time you printed, or the printer would merrily empty itself of paper creating a huge stack of Liddas for you.
Anyway, this was before DDI and before the character builder. So making those PCs one at a time was a handcrafted effort. My mandate was to make straightforward but not suboptimal choices. Tordek, for example, was a sword-and-board (OK, sword and axe) fighter rather than some sort of spiked-chain wunderkind. I wanted any intermediate-level D&D player to be able to sit down and play a Pre-Fab Four character right away.
Make characters from level 1 to level 20 four times in a row—gear and all—and you get good at it, eventually. (Or at least you get more efficient.) But it still took hours…maybe a day for the nonspellcasters and more than that for Mialee and Jozan. Nowadays DDI and a less gear-centric game would make it a lot faster…except that there are 30 levels now.
Handcrafting the Pre-Fab Four made me a lot more aware of what each class was capable of, which items, feats, and spells were key…all sorts of stuff. And I'm pretty sure that a similar effort in 4e would make anyone a better D&D player.
Do It Yourself
So here's one way to get better at D&D: Take your favorite character class and build it one level at a time, gear and all, until you hit 30th level. Trust me: You will become an utter brainiac about your class.
Alternatively, pick a specific level—5th and 11th are solid choices—and make characters at that level for lots of classes. Try making a 5th-level character for the class of every other player at your table. You'll be amazed at how much you learn about your buddies' PCs. You will become Mr. Teamwork at your table.
I'd suggest that rather than going for esoteric builds, you stick with "straightforward and solid choices." Remember, you're doing this to learn, not to "win" at D&D with your extreme power-munchkin-sauce.
Don't stress out too much about the choices you make. That's not the point. The point is to put yourself in assessment mode—to feel the "this power or that power?" question at each level. If you do that, you learn about both the options you chose and the options you didn't choose.
And look at it this way: Your choices will certainly be better than the DDI Character Creator's Auto-Pick function! (Seriously, they should just turn that function off. No guidance is better than horrible, misleading guidance.)
Out of Context: Don't you dare call me toffee-nosed!
Music: Black Crowes, Amorica